Core scientific use cases
In the course of the next 6 years, EXCLAIM develops the corresponding performant model versions and runs them to demonstrate the ability of the platform to reach the specified targets. The number of model versions will be minimized to ensure that throughout the project a small set of ICON versions with increasing computational performance are available. Thorough testing will ensure that these versions will be functionally equivalent despite transiting from FORTRAN+ to a Python-based framework.
Aqua Planet
Aqua Planet simulations depict the simplest representation of the Earth's climate on a sphere, including its major large-scale atmospheric circulation. The use case will consist of a series of simulations with increasing resolution up to 1 km horizontal grid spacing in order to assess the response in radiative forcing, atmospheric circulation features and the water cycle to a uniform warming of the sea-surface. The configuration allows assessing two central hypotheses: Convergence of the cloud radiative feedbacks at kilometer scale resolution, and the robustness of the model formulation. This configuration also allows us to assess the quality of the representation of the mid-latitude storm tracks, which in current state-of-the-art climate models are significantly biased. Aqua Planet simulations are also an ideal contribution to ensure the efficacy, consistency and accuracy of the ICON development in the transition phase from FORTRAN to Python.
Global uncoupled simulations for clouds and convection
Kilometer-scale horizontal resolution offers promising prospects for improved simulations of convective clouds. A series of multi-year km-scale simulations with prescribed Sea Surface Temperatures (SSTs) are envisaged. The simulations will use explicit convection and be evaluated in comparison to lower-resolution simulations using parameterized convection. To investigate the effects of changes in climate-relevant forcings and boundary conditions in km-scale simulations, a time-slice approach will be pursued. Thereby, the observed SSTs and sea-ice distributions are superimposed with corresponding climate-change signals derived from transient climate simulations with coupled atmosphere-ocean global climate models such as available from the Coupled Model Intercomparison Project phase 6 (external pageCMIP6call_made) or from the external pageHAPPIMIPcall_made project, representative for global warming levels of 2°C or 4°C.
Global coupled climate simulations for extremes
The final step up the complexity chain are global simulations with the fully coupled (atmosphere, ocean, sea-ice, land surface) climate model. A core scientific theme driving this scientific use case are extremes, especially those that have a connection to the oceanic realm, such as tropical cyclones, marine heatwaves and their extension over land regions. With extremes being rare by nature, the baseline simulations need to extend over a few decades. The horizontal resolution will be progressively increased from ~25 km to order of 3 kilometers later in the project.
Regional European climate simulations for scenarios
Climate scenarios at local to regional scales are an indispensable backbone for the development of effective adaptation strategies and for assessing the local and regional climatic effects of different mitigation options. To this end, a regional climate (limited area) implementation will be developed in EXCLAIM on the basis of the uncoupled global setup benefiting from the development of the ICON-22 project at MeteoSwiss. In the first phase, the focus will be on the conventional external pageEURO-CORDEXcall_made resolution of around 12 km, increasing in the second phase the resolution to 1 km, thereby providing the full potential of very fine-scale regional climate scenarios for Alpine domains.